1. Field of the Invention
The present invention relates to a semiconductor device that uses a crystalline semiconductor film obtained through crystal growth on an insulating surface by using a laser light and uses a field effect transistor, more particularly, a thin film transistor and to a manufacturing method therefor.
2. Description of the Related Art
Conventionally, a semiconductor display device as an example of semiconductor devices has a drive circuit formed on a silicon substrate, which is connected to a pixel portion on a glass substrate via an FPC and the like. However, ICs are connected to the glass substrate on which the pixel portion is formed via the FPC and the like, there arises a problem in that a connected portion is weak against any physical impact. In particular, as the number of pins of the FPC increases, there is growing tendency for the connected portion to exhibit a poor property against the physical impact.
Then, techniques of integrating a drive circuit and a controller of the semiconductor display device with the pixel portion on the same glass substrate (system on glass) have been put into active research and development. The realization of the system on glass makes it possible to avoid the aforementioned problem by reducing the number of pins of the FPC as well as to reduce a size of the semiconductor display device itself.
For example, in a case of an active matrix liquid crystal display device as an example of the semiconductor display devices, a scanning line drive circuit and a signal line drive circuit are formed on the same glass substrate, the scanning line drive circuit being used for sequentially selecting one or more pixels among the plural pixels formed in the pixel portion and the signal line drive circuit being used for inputting signals (video signals) having image information to the selected pixels. This makes it possible to enhance resistance to the physical impact in the liquid crystal display device and to reduce the size of the liquid crystal display device itself.
Further, in recent years, integral formation of the controller, which has been conventionally formed on the silicon substrate, on the glass substrate, is being attempted in addition to the drive circuit. If both of the controller and the drive circuit can be integrally formed on the glass substrate on which the pixel portion is formed, the size of the semiconductor display device can be remarkably reduced and the resistance to the physical impact can be further enhanced.
However, the controller has a function of generating signals for determining timings at which the drive circuit or pixel portion operates, that of processing the video signals within a predetermined standard supplied from an external video source in accordance with specifications of the drive circuit or pixel portion, and the like. Therefore, the controller itself should be designed newly each time the standard and the specification of the semiconductor display device or driving methods therefor change.
For example, in the case where there is a demand for manufacturing various types of trial products while the design for the controller is changed or the design therefor should be changed for each client, when the controller is integrally formed on the glass substrate with the drive circuit and the pixel portion, all masks including those for the pixel portion and the drive circuit must be changed for each case. This makes it difficult to suppress a manufacturing cost of the semiconductor display device.
Particularly in recent years, the semiconductor display devices have been used in display portions of various electronic devices, which accelerates the tendency toward high-mix low-volume production. Therefore, if the controller is integrally formed on the glass substrate, the design change of the controller involves the increase in cost as described above, which is expected to lead to a serious problem.